The invention relates to improvements in apparatus for making perforations in running webs of paper or other wrapping material for use in connection with the production of cigarettes and/or other smokers' products. More particularly, the invention relates to improvements in apparatus for electrically perforating running webs of tipping paper or the like.
Filter tipping machines are normally equipped with apparatus for making perforations in webs which are thereupon subdivided into uniting bands serving to sealingly connect plain cigarettes with filter mouthpieces of desired length. Many presently known perforating apparatus include perforating units with pairs of holders for sets of electrodes which are connectable to a source of high voltage in order to generate sparks which burn away portions of the running web. The latter is advanced between the holders. Reference may be had, for example, to commonly owned U.S. Pat. Nos. 4,247,754 and 4,323,082, and to commonly owned published German patent application No. 32 03 103.
Apparatus of the above outlined character separate fragments of paper from selected portions of the running web. The separated fragments deposit on the electrodes and thus affect the quality of the perforating operation. Attempts to prevent the separated fragments from adhering to the electrodes include changing the polarity of the applied voltage. This merely reduces the rate at which the fragments gather on the electrodes so that the perforating apparatus must be cleaned at less frequent intervals than in the absence of changes of polarity. Nevertheless, it is necessary to shut down the perforating apparatus at certain intervals in order to permit a thorough cleaning of the electrodes and to thus ensure that the perforating operation will result in the making of a desired number of holes, i.e., in a desired increase of permeability of the web. Each interruption of operation of the perforating apparatus necessitates a stoppage of the entire machine in which the apparatus is put to use. This is highly undesirable in modern filter tipping machines which turn out many thousands of filter cigarettes or analogous smokers' products per minute. In addition, each stoppage of the filter tipping machine might necessitate a stoppage of other machines in the production line which includes a filter tipping machine. Such production line further includes one or more cigarette makers, a packing machine and a machine which provides cigarette packs with transparent outer envelopes.